Method and device for operating an internal combustion engine in the event of a fault in a crankshaft sensor

ABSTRACT

A method for operating an internal combustion engine in the event of a fault in a crankshaft sensor is provided, the internal combustion engine having at least two camshafts and a speed and/or a position of the internal combustion engine being derived from a signal taken from the camshaft. In order to improve the exhaust gas performance of the internal combustion engine even in a crankshaft emergency operating mode, only a first camshaft is used to determine the speed and/or the position of the internal combustion engine, while the second camshaft. is adjusted in its angle of rotation in order to set a variable valve operating mechanism on the intake and exhaust valves of the internal combustion engine that are driven by the second camshaft.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for operating an internal combustion engine in the event of a fault in a crankshaft sensor, the internal combustion engine having at least two camshafts and a rotational speed and/or a position of the internal combustion engine being derived from a signal taken from the camshaft, and to a device for implementing the method.

2. Description of the Related Art

In today's motor vehicles it is important to determine the speed of the internal combustion engine precisely since this parameter enters into numerous open-loop and closed-loop control processes of the motor vehicle. Usually, this speed is derived from the rotational speed of a crankshaft, which is driven by the mechanical energy generated in the combustion process. For this purpose, the crankshaft is scanned by a crankshaft sensor, which detects the speed and position of the crankshaft. The signal is provided by a suitable sensor, which is evaluated in a control unit as a measure for the speed and/or the position of the internal combustion engine. In the process, the injection and ignition point of the internal combustion engine is determined.

In the event of a failure or a fault of the crankshaft sensor signal, the control unit switches to a crankshaft emergency operating mode, in which the position of the internal combustion engine is determined from the position of a camshaft, which is likewise driven by the crankshaft. A precondition for this crankshaft emergency operating mode is that the camshafts must be fixed in a certain position with respect to the crankshaft so that it is possible to determine the position of the internal combustion engine precisely. The camshafts are thus no longer available for a camshaft adjustment in the various operating ranges of the internal combustion engine, which results in a deterioration of the exhaust gas performance of the internal combustion engine.

BRIEF SUMMARY OF THE INVENTION

The present invention is thus based on the objective of indicating a method and a device for operating an internal combustion engine in the event of a fault or the failure of a crankshaft sensor, in which the exhaust gas performance of the internal combustion engine is improved even in a crankshaft emergency operating mode.

According to the present invention, the objective is achieved by the fact that only a first camshaft is used to determine the speed and/or the position of the internal combustion engine, while the second camshaft is adjusted in its angle of rotation in order to set a variable valve operating mechanism on the intake and exhaust valves of the internal combustion engine that are driven by the second camshaft. This has the advantage that the speed and/or position of the internal combustion engine determined during the crankshaft emergency operating mode may be determined reliably and precisely by a single camshaft. In addition, variable valve opening times continue to be set with the aid of the second camshaft. Turning the second camshaft out of its original position improves the exhaust gas performance of the internal combustion engine, the positive influence on the exhaust gas performance remaining in effect even during the crankshaft emergency operating mode. The adjustment of the valve opening times allows for an increase in the efficiency of the internal combustion engine, which is shows its effect in a performance and torque gain or a reduction in fuel consumption.

Advantageously, the first camshaft assumes a reference position with respect to a crankshaft driven by the internal combustion engine and rotates in a specified transmission ratio with respect to the crankshaft, the rotary motion of the camshaft being detected by a camshaft sensor. Setting the reference position effects a fixed and unambiguous association of the motion of the camshaft in relation to the motion of the crankshaft such that this may be used to determine the position of the internal combustion engine reliably.

In one variant, the first camshaft situated in the reference position with respect to the crankshaft opens and/or closes the exhaust valves of the internal combustion engine, while the second camshaft that has been turned out of its original position opens and/or closes the intake valves of the internal combustion engine. In a camshaft adjustment, the intake and exhaust valve control times are changed as a function of the rotational speed in order to achieve the most efficient cylinder charge in all speed ranges. The desired effect of the exhaust gas reduction may already be achieved solely by turning the camshaft that controls the intake valves out of its original position. One camshaft thus suffices for setting the variable valve operating mechanism.

In one development, when more than two camshafts are used, only the first camshaft is held in the reference position with respect to the crankshaft, while the remaining camshafts are adjusted in their angle of rotation. Since, with the exception of one camshaft, all other camshafts are available for actuating the intake and/or exhaust valves, it becomes possible to achieve an optimized setting of the variable valve operating mechanism, which is reflected in an improved exhaust gas performance of the internal combustion engine in the crankshaft emergency operating mode. When using multiple camshafts, an adjustment is made not only to an intake camshaft, but also to an exhaust camshaft, which controls the exhaust valves of the internal combustion engine. Such an adjustment of the exhaust camshaft additionally allows for a variation of the internal exhaust gas recirculation in the form of reducing the nitrogen oxide emission. In addition, the simultaneous adjustment of the intake and exhaust camshafts increases the possibility that the opening times of the intake and exhaust valves will overlap, which results in an even better optimization of the gas streams in the internal combustion engine.

Furthermore, the camshafts are adjusted in their angle of rotation as a function of the speed of rotation and/or the position of the internal combustion engine detected by the camshaft sensor. Since the adjustment of the camshaft effects a change in the angle of rotation in relation to the crankshaft and since this adjustment depends on the ascertained speed of the internal combustion engine, in the event of a crankshaft emergency operating mode, the angle of rotation is ascertained as a function of the speed determined with the aid of the first camshaft.

In one development, in the adjustment of its angle of rotation, the camshaft driven by the crankshaft is shifted from its specified position with respect to the crankshaft so as to change the control times of the intake or exhaust valves of the internal combustion engine. This adjustment occurs simply in a mechanical manner since a hydraulic phase adjuster is situated between the crankshaft and the camshaft, which is situated at the end of each camshaft for transmitting force.

In another specific embodiment, the adjustment of the second camshaft occurs between two permanently defined angles of rotation within an adjustment range of the second camshaft. This reduces the control effort required for the phase adjuster. The adjustment range typically amounts to 60° of the crankshaft.

Alternatively, the adjustment of the second camshaft occurs steplessly within the adjustment range of the camshaft. Although it requires an elaborate control process, the stepless adjustment of the camshaft makes it possible to react comfortably to various operating states of the internal combustion engine and thus to adjust the exhaust gas performance of the internal combustion engine advantageously.

A further development of the present invention relates to a device for operating an internal combustion engine in the event of a fault in a crankshaft sensor, the internal combustion engine having at least two adjustable camshafts and a rotational speed and/or the position of the internal combustion engine being ascertained from a signal taken from the camshaft rotation. In order to improve the exhaust gas performance of the internal combustion engine even in a crankshaft emergency operating mode, only a first camshaft is used to determine the speed of the internal combustion engine, while means are provided for adjusting the second camshaft in its angle of rotation in order to set a variable valve operating mechanism on the intake or exhaust valves of the internal combustion engine that are driven by the second camshaft. This system brings about an improvement of the exhaust gas performance of the internal combustion engine even in the crankshaft emergency operating mode.

In one development, the first and the second camshaft are controlled in their respective rotary motion by a control unit, the control unit, which sets the first camshaft in a reference position with respect to the crankshaft, is connected to a camshaft sensor that detects the rotary motion of the first camshaft, from which the control unit determines the speed and/or the position of the internal combustion engine and as a function of the ascertained speed or position of the internal combustion engine controls an adjusting device connected to the second camshaft for turning the angle of rotation of the second camshaft out of its original position. In addition to determining precisely the position and/or speed of the internal combustion engine using only one camshaft, variable valve opening times are set using the second camshaft even in a crankshaft emergency operating mode. Turning the second camshaft out of its original position improves the exhaust gas performance of the internal combustion engine by optimizing the ratio of fresh air and fuel, the positive influence on the exhaust gas performance remaining in effect even in the crankshaft emergency operating mode. A suitable actuating mechanism is used as an actuator, which operates electrically or hydraulically and performs this adjustment simply in a mechanical manner, and which for transmitting force is situated at the end of each camshaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the basic structure of a V-shaped internal combustion engine having 4 camshafts.

FIG. 2 shows a basic representation for situating a crankshaft sensor and a camshaft sensor in a V-shaped internal combustion engine as shown in FIG. 1.

FIG. 3 shows a camshaft including a camshaft adjuster.

DETAILED DESCRIPTION OF THE INVENTION

Identical features are indicated by the same reference symbols.

FIG. 1 shows a basic representation of an internal combustion engine 1 in the shape of a V. In this instance, cylinders 2 of internal combustion engine 1 are arranged in a v-shape on two planes 3, 4, a crankshaft 5 being situated at the intersection of the two planes 3, 4. Each plane 3, 4 is typically called a bank. Each cylinder 2 is equipped with one or more intake valves 6 and one exhaust valve 7. Fresh air and fuel are conveyed through intake valve 6 into the respective cylinder 2 of internal combustion engine 1, while the combustion products of cylinder 2 in the form of exhaust gas are discharged from internal combustion engine 1 via exhaust valve 7. Intake valves 6 of first plane 3 of cylinders 2 are connected to a first camshaft 8, while exhaust valves 7 of first plane 3 are operated by a second camshaft 10. Analogously, intake valves of second plane 4 of cylinders 2 connect to a third camshaft 9, and exhaust valves 7 of second plane 4 work together with a fourth camshaft 11. Each camshaft 8, 9, 10, 11 has an eccentric cam (protrusion) for each valve 2, which cam is not shown. Since the camshaft rotates about its own axis, this rotary motion being converted into a short longitudinal movement by the cam, the intake or exhaust valve 6, 7 associated with the cam is opened. As the cam continues to rotate, valve 6, 7 is closed again by a valve spring 19 (FIG. 3).

A speed sensor wheel 12 in the form of a toothed wheel is situated at one end of crankshaft 5, which is shown in FIG. 2 next to the sketched internal combustion engine 1. Speed sensor wheel 12 has a defined number of teeth 13 made of iron or steel, which are arranged continuously on the circumference of speed sensor wheel 12 and are interrupted by one gap or multiple gaps 14. A crankshaft sensor 15 is situated across from speed sensor wheel 12, which scans the teeth and the gap(s) 14 in that a magnetic field, which crankshaft sensor 15 spans using a magnet, is interrupted by teeth 13, whereby an alternating voltage is induced in a coil of crankshaft sensor 15, which the latter transmits to a control unit 16 for analysis. Gap 14 of crankshaft sensor wheel 12 signals that crankshaft 5 has completed one turn, which indicates the end of a working cycle of a cylinder 2.

A camshaft sensor wheel 17 is situated on each camshaft 8, 9, 10, 11, which is shown in FIG. 2 only in the example of camshaft 9. This camshaft sensor wheel 17 also has teeth that are interrupted by gaps. Camshaft sensor wheel 17, however, is not subdivided in as differentiated a manner as crankshaft sensor wheel 12, which has 60 -2 teeth, while camshaft sensor wheel 17 in the present example has only 3 teeth.

Camshafts 8, 9, 10, 11 are driven by crankshaft 5 via a transmission (not shown), the transmission having a transmission ratio such that camshafts 8, 9, 10, 11 only rotate half as fast as crankshaft 5.

In order to vary the control time of the intake and exhaust valves by camshaft 8, 9, 10, 11, the respective camshaft 8, 9, 10, 11 is turned by a certain angle out of its original position with respect to crankshaft 5. The adjustment of camshaft 8, 9, 10, 11 occurs as a function of the rotational speed of internal combustion engine 1 and means that the opening of the intake or exhaust valve 6, 7 is changed with respect to the crank angle of crankshaft 5. For this purpose, a hydraulic camshaft adjuster 20 is used, for example, as is shown in FIG. 3 in connection with camshaft 9. As already explained, a toothed wheel 21 of the transmission turns camshaft 9. Camshaft adjuster 20, which is likewise connected to control unit 16 and is controlled by the latter, shifts the position of camshaft 9 with respect to toothed wheel 21 such that valve 2 is closed earlier or later, whereby an increase in the efficiency of internal combustion engine 1 is achieved.

In particular overlaps in the opening times of the intake and exhaust valves fundamentally influence the characteristics of internal combustion engine 1. An internal combustion engine 1 having little overlap has a rather high torque at low rotational speeds. By great overlaps it is possible to achieve a higher maximum performance of internal combustion engine 1.

If it is now determined that crankshaft sensor 5, by which not only the speed of internal combustion engine 1 is determined, but also its position, provides an output signal with high interference or no signal at all, then control unit 16 will switch into a so-called crankshaft emergency operating mode. In this crankshaft emergency operating mode, one of the four camshafts 8, 9, 10, 11 of internal combustion engine 1 is brought into a reference position with respect to crankshaft 5. In the present example, this is camshaft 11, which controls exhaust valves 7 of second plane 4 of cylinders 2. This reference position creates a fixed relationship between the motion of crankshaft 5 and of camshaft 11, whereby the engine position may be determined in a defined manner. A camshaft sensor wheel 17 is situated at one end on this camshaft 11 as well, which has a camshaft sensor 18 across from it (FIG. 2). The magnetic field of the camshaft sensor 15, which is developed as a Hall sensor, is modified by the individual teeth of camshaft sensor wheel 17, which is transmitted as a signal to control unit 16, which derives the speed and position of internal combustion engine 1 from this signal.

The remaining three camshafts 8, 9, 10, which are not needed for determining the position and speed of internal combustion engine 1, are available for adjustment, whereby the exhaust gas performance of internal combustion engine 1 is improved by controlling the two intake camshafts 8, 9 and the remaining exhaust camshaft 10. Because of the fact that multiple camshafts are available for adjustment in the already described manner, intake and exhaust control times may be set that bring about a most efficient cylinder charge in all speed ranges of internal combustion engine 1. 

1-10. (canceled)
 11. A method for operating an internal combustion engine having at least two camshafts in the event of a fault in a crankshaft sensor, comprising: determining at least one of a speed and a position of the internal combustion engine based on a signal from only a first camshaft; and adjusting an angle of rotation of a second camshaft in order to set a variable valve operating mechanism on intake valves and exhaust valves of the internal combustion engine which are driven by the second camshaft.
 12. The method as recited in claim 11, wherein the first camshaft assumes a reference position with respect to a crankshaft driven by the internal combustion engine and rotates in a specified transmission ratio with respect to the crankshaft, the rotary motion of the first camshaft being detected by a camshaft sensor.
 13. The method as recited in claim 12, wherein the first camshaft which is in the reference position with respect to the crankshaft at least one of selectively opens and closes the exhaust valves of the internal combustion engine, and wherein the second camshaft which has been adjusted at least one of selectively opens and closes the intake valves of the internal combustion engine.
 14. The method as recited in claim 12, wherein at least three camshafts are provided, and wherein the respective angles of rotation of the second and third camshafts are adjusted.
 15. The method as recited in claim 14, wherein the respective angles of rotation of the second and third camshafts are adjusted as a function of at least one of the speed of rotation of the internal combustion engine and the position of the internal combustion engine detected by the camshaft sensor.
 16. The method as recited in claim 15, wherein, in the adjustment of the respective angles of rotation, the second and third camshaft driven by the crankshaft are each shifted from a specified position with respect to the crankshaft so as to change the control times of at least one of the intake and exhaust valves of the internal combustion engine.
 17. The method as recited in claim 13, wherein the adjustment of the second camshaft occurs between two permanently defined angles of rotation within an adjustment range of the second camshaft.
 18. The method as recited in claim 17, wherein the adjustment of the second camshaft occurs in a step-less manner within the adjustment range of the camshaft.
 19. A control device for operating an internal combustion engine having at least two camshafts in the event of a fault in a crankshaft sensor, comprising: means for determining at least one of a speed and a position of the internal combustion engine based on a signal from only a first camshaft; and means for adjusting an angle of rotation of a second camshaft in order to set a variable valve operating mechanism on intake valves and exhaust valves of the internal combustion engine which are driven by the second camshaft.
 20. The device as recited in claim 19, wherein: a control unit controls respective rotary motions of the first and second camshafts; the control unit sets the first camshaft in a reference position with respect to the crankshaft; the control unit is connected to a camshaft sensor which detects the rotary motion of the first camshaft; the control unit determines the at least one of a speed and a position of the internal combustion engine based on an output signal of the camshaft sensor; and the control unit controls, as a function of the determined speed of the internal combustion engine, an adjusting device connected to the second camshaft for adjusting the angle of rotation of the second camshaft from an original position. 